1. Field of the Invention
The present invention relates to valve adapters and more specifically to a valve adapter used to prevent thread mismatch on a marine installation.
2. Description of the Related Art
NPS (National Pipe Straight) threads are intended to provide a loose mechanical joint between similarly threaded components, and are not capable of providing a watertight seal. NPT (National Pipe Taper) threads are intended to provide a watertight joint between similarly threaded components.
There are two common types of ball valves employed in the marine industry: in-line valves that are provided with NPT thread at each end, and flanged valves (seacocks) which include an NPT thread at an outlet end and an NPS thread at a flanged inlet end. NPS threads are used at the flanged inlet end of seacocks and on thru-hull fittings because of the variable thickness of vessel hulls through which the thru-hull fitting must pass before threading into the flanged seacock. Flanged seacocks are desirable for below waterline use because the flange portion of the valve spreads the mechanical load over a greater area, thus providing increased support for the valve and the connected components. Flanged seacocks are generally attached to a boat hull at the flange with fiberglass, adhesives, and/or mechanical fasteners to strengthen the installation. However, it is extremely difficult to remove a seacock installed in this manner from the boat hull as may be necessary to replace the seacock.
The less costly in-line valve design is suitable for and most commonly employed in inboard systems (fuel systems, water pressure systems, etc.). In-line valves are not recommended for through-the-hull use, but are often improperly used in below waterline through-the-hull applications by screwing them directly onto a standard thru-hull fitting. This creates a threads mis-match (NPS of the fitting into NPT of the valve), resulting in unsafe minimal thread engagement between the two incompatible components. Additionally, the use of an in-line valve in this manner provides inadequate structural strength because the flangeless in-line valve and connected components are supported only by the NPS-threaded thru-hull fitting and the amount of engagement (only a few threads) between the two components.
An improved system is required that provides the strength of a seacock valve system and the easy replacement of an in-line valve system.